A Dense Wavelength Division Multiplexed (DWDM) optical transmission system allows multiple signals to communicate on a single pair of optical fibers. DWDM systems have been adopted by telecommunication vendors to route signals throughout communications networks. In modern telecommunication systems, an optical power level up to 10 mW is considered safe for human eyes. However, power levels in optical fibers used for telecommunication applications normally exceed this value. For example, a commonly used Erbium Doped Fiber Amplifier (EDFA) emits a power level of more than 20 dBm (200 mW). When all fibers are connected, transmission at high power levels is not an issue. But in the event of a fiber cut/disconnection, for safety reasons, optical power levels need to be reduced very quickly below the 10 mW limit.
The power levels can be restored to greater than 10 mW only when all fibers are re-connected properly, with no possibility that an optical light beam could injure a human. There are strict requirements for power reduction and restoration in terms of timing and reliability of the mechanisms.